<template>
  <div class="spec-preview">
    <!-- 小图 -->
    <img :src="image.imgUrl" :alt="image.imgName" />
    <!-- 遮罩小图的容器 -->
    <div class="event" @mousemove="move"></div>
    <!-- 大图 -->
    <div class="big">
      <!-- 
        系数 2 = 大图宽度 / 小图宽度
       -->
      <img
        :src="image.imgUrl"
        :alt="image.imgName"
        :style="{
          left: -2 * left + 'px',
          top: -2 * top + 'px',
        }"
      />
    </div>
    <!-- 小绿块 -->
    <div
      class="mask"
      :style="{
        left: left + 'px',
        top: top + 'px',
      }"
    ></div>
  </div>
</template>

<script>
import throttle from "lodash/throttle";

export default {
  name: "Zoom",
  props: {
    image: {
      type: Object,
      default: () => ({}),
    },
  },
  data() {
    return {
      left: 0,
      top: 0,
    };
  },
  methods: {
    move: throttle(function(event) {
      // 计算小绿块的位置
      // left = 鼠标offsetX- 小绿块宽度的一半（100）
      let left = event.offsetX - 100;
      if (left < 0) left = 0;
      if (left > 200) left = 200;
      // top = 鼠标offsetY - 小绿块高度的一半（100）
      let top = event.offsetY - 100;
      if (top < 0) top = 0;
      if (top > 200) top = 200;

      this.left = left;
      this.top = top;
    }, 1000 / 60),
  },
};
</script>

<style lang="less">
.spec-preview {
  position: relative;
  width: 400px;
  height: 400px;
  border: 1px solid #ccc;

  img {
    width: 100%;
    height: 100%;
  }

  .event {
    width: 100%;
    height: 100%;
    position: absolute;
    top: 0;
    left: 0;
    z-index: 998;
  }

  .mask {
    width: 50%;
    height: 50%;
    background-color: rgba(0, 255, 0, 0.3);
    position: absolute;
    left: 0;
    top: 0;
    display: none;
  }

  .big {
    width: 100%;
    height: 100%;
    position: absolute;
    top: -1px;
    left: 100%;
    border: 1px solid #aaa;
    overflow: hidden;
    z-index: 998;
    display: none;
    background: white;

    img {
      width: 200%;
      max-width: 200%;
      height: 200%;
      position: absolute;
      left: 0;
      top: 0;
    }
  }

  .event:hover ~ .mask,
  .event:hover ~ .big {
    display: block;
  }
}
</style>
